Heat the oven to 400°F (200°C). Line a rimmed baking sheet with foil, set a wire rack on top, and lightly grease the rack so the bacon-wrapped meatballs release easily after baking.

In a large bowl, combine the ground beef, Italian sausage, egg, breadcrumbs, Parmesan, garlic, onion, Worcestershire sauce, parsley, kosher salt, and black pepper. Mix only until the ingredients are evenly combined; overmixing can make the meatballs dense.

Divide the meat mixture into 16 portions. Flatten one portion slightly, place a mozzarella cube in the center, and carefully seal the meat completely around the cheese so there are no openings for the filling to escape.

Wrap each meatball with half of a bacon slice, keeping the bacon snug but avoiding heavy overlap. Position the bacon seam underneath, then place the meatballs on the prepared rack with space between each one.

Bake for 20–25 minutes, turning the meatballs once if needed so the bacon browns evenly. Continue cooking until the bacon is browned and the center of the meatballs reaches at least 160°F (71°C) on an instant-read thermometer.

Brush the meatballs with barbecue sauce during the final 3–5 minutes of baking, or serve the sauce on the side. If the bacon needs additional color, broil for 1–2 minutes while watching closely to prevent scorching.

Remove the meatballs from the oven and let them rest for 5 minutes before serving. This short rest allows the hot cheese to settle slightly and helps the meatballs stay juicy when bitten into.